body{
    background-image: url("../img/menu.jpg");
    background-repeat:no-repeat ;
    background-size: cover;
    background-attachment: fixed;
}
.mainIndex{
    width: 50%;
    height: 50%;
    text-align: center;
    position: absolute;
    left: 50%;top: 50%;
    transform: translate(-50%,-50%);

}